Circular Pin Research Articles

Analytical and experimental investigations of optimum thermomechanical conditions to use tools with non-circular pin in friction stir welding

Friction stir welding tools with non-circular pins exhibit comparatively superior weld quality than circular pins. Improper selection of process parameters directs towards excess or insufficient heat supply which deteriorates weld quality and tool life. This necessitates exact prediction of heat generation with respect to the chosen pin geometry that is required to optimise process parameters. In this paper, a novel analytical model is developed to quantify the percentage reduction in heat generation on the replacement of circular tool pin with non-circular. Experiments were conducted using tools with different pin geometries to validate the proposed model. Based on the obtained results, optimum process variable selection charts were prepared with respect to the reduction in heat supply to facilitate amiable environment to use non-circular tool pins. Weld quality on the suggested range in the charts was examined through macro structure, hardness and tensile analysis.

STATIC THERMAL ANALYSIS OF FINS MODELS USING ANSYS

The Engine chamber is one of the essential engine components, that is subjected to over the top temperature differences and thermal stresses. Fins are set on the surface of the cylinder to improve the quantity of heat exchange by convection. When fuel is burned in an engine, heat is produced. Additional heat is also generated by friction between the moving parts. In air-cooled I.C engine, extended surfaces called fins are provided at the periphery of engine cylinder to increase heat transfer rate. That is why the analysis of fin is important to increase the heat transfer rate. The main of aim of this work is to study various researches done in past to improve heat transfer rate of cooling fins by changing cylinder fin geometry and material. In the present work, Experiments have been performed to discover the temperature variations inside the fins made in four kind geometries (plate Fins, Circular Pin fins, plate fins with holes, and draft Pin fins) and consistent state heat exchange examination has been studied utilizing a finite element software ANSYS to test and approve results. The temperature variations at various areas of fins models are evaluated by FEM and compared models of fins performance by heat flux and temperature variations obtained by experimentally in Analysis. The principle implemented in this project is to expand the heat dissipation rate by utilizing the wind flow. The main aim of the study is to enhance the thermal properties by shifting geometry, material, and design of fins.

Research on the mechanism of heat transfer enhancement in microchannel heat sinks with micropin fins

In this paper, the pressure drop and heat transfer features of a microchannel applying micropin fins are investigated by numerical simulations and experiments. The microchannel, which is 20-mm long, 2.7-mm wide, and 0.3-mm deep, is fabricated with copper and consisted of staggered diamond micropin fins. The visualization experiments, by means of the advanced technology micro-particle image velocimetry (PIV), are conducted to discuss the mechanism of heat transfer by analysing the flow regimes. Meanwhile, 3D-coupled numerical simulations are applied for the combination with experiments in this research. It is found that the vortex-wake flow is stable at Reynolds number (Re) = 0 to 300, and a steady recirculating zone can be observed in the wake, where a pair of symmetrical vortices is formed. All the time, the vortex-wake flow is unstable at Re = 300 to 650. Under this situation, it is due to the decrease of vorticity that the Nusselt number (Nu) is not significantly increased as it was expected. Thus, when Nu in the pin fin microchannel is predicted, the vorticity should be considered as well as turbulent kinetic energy (TKE). Furthermore, comparative study was carried out based on the mechanism proposed in this study among three kinds of microchannel with different fins, including staggered circular pin fins (CPF), square pin fins (SPF), and diamond pin fins (DPF).

A comparative study on role of phase change materials in thermal efficiency enhancement of passive solar still

Solar still is a feasible technical process to change the saline water in to drinking water economically. The main problem in solar still is the thermal energy dissipation from walls of the SS basin and consequently it reduces the performance of the solar desalination system. A PCM will be a suitable remedy and it absorbs heat during day time and can be utilized during non availability of solar radiation. This article explains the technique of utilizing PCM in SS and productivity enhancement of still due to utilization of phase change material. Different PCM's in SS are investigated in this review and the results reveals that the paraffin wax PCM posses maximum output amongst palmitic acid, myristic acid, lauric acid, capric acid, bees wax, bitumen, capric acid and stearic acid. The utilization of paraffin wax enhances the exergy efficiency, energy efficiency and productivity of a passive SS by 40%, 67% and 180%. Incorporation of paraffin wax in the void circular pin fins has emerged as efficient method to enhance the thermal conductivity (K) value. This method enhances energy efficiency and yield of SS by 37.50% and 12%.

Effects of tool pin profile on tensile and wear behaviour of friction stir welded AA6101-T6 and AA1350 alloys

In Friction Stir Welding (FSW) technique, hard rotating tool with specially profiled pin is plunged into base metals and traversed along the interface of the plates, generating the frictional heat and plasticizing the base metals. This leads to flow of materials and makes solid state joint. AA6101-T6 and AA1350 alloys are widely applied in electrical bus bars, because of their high electrical conductivity. In this present work, these two alloys are joined by varying the pin profile of the tools as circular, triangular, square and hexagonal. Of these four joints, the joint fabricated by circular pin profiled tool exhibits poor tensile and wear properties whereas hexagonal pin profiled tool exhibits better tensile and wear properties. This is due to the volume defects and grain refinement at stirred zone.

Model ulaza prolazne toplote kod zavarivanja trenjem sa mešanjem korišćenjem nekružne igle alata

Frictional heat source in the contact surface of a rotating tool and a stationary work piece is used to join metal pieces along the weldline in the friction stir welding process. Temperature profile developed during welding decides the post weld properties on the joined work pieces not only along the weld line but also in the nearby layers of heat affected zone. As the heat input depends on the contact surface geometry in the tool/matrix interface, tool shape has a higher influence on peak temperature developed during the process and on the other hand it influences the post weld properties also. In this paper, a simplified analytical heat input model has been derived and validated for noncircular pin profile by introducing a new multiplication factor in the circular pin profile heat input model. Transient thermal numerical models are developed for, triangular, square and pentagonal pin profiles using analytical heat input results to analyse the change in temperature profiles with respect to the change in tool pin geometry. Furthermore, a detailed analysis is made to understand the percentage contribution of tool pin on the total heat supply.

Experimental investigation of the cooling performance of 3-D printed hybrid water-cooled heat sinks

An experimental characterization of hybrid water-cooled heat sinks for multi-core CPUs was conducted. The hybrid heat sinks consist of a water block containing fractal channel manifolds ending in an array of jet nozzles attached to a copper plate. Advanced additive manufacturing techniques were required for the fabrication of the heat sinks due to the manifolds complexity. The effects of the jet nozzles number and distribution, depth of the flood chamber, and surface enhancing features were investigated in terms of hydraulic and thermal performance. A minimum pressure drop variation was observed for different number of jet nozzles (16, 32, and 64 jets), which is consistent with previous simulation results. Alternatively, the pressure drop associated with a 3-mm size reduction of the flood chamber generated a two-fold increase in the pressure drop difference, but under 5% of the total pressure drop. A sharp temperature increase (~30 °C) was observed from idle operation within 10 s after applying a full load on the CPU and the system reached steady state in ~74 s. The highest core temperature was observed using the heat sink with 32 jets, while the heat sinks with 16 and 64 jets had similar thermal performance. Area enhancing features added to the copper plate produced negligible effects on the hydraulic performance, while average core temperature reductions up to 3 °C were measured using circular pin fins. To further analyze the thermo-hydraulic performance, the thermal resistance and the pumping power were calculated. The overall performance assessment was conducted using a metric formed by the combination of the thermal resistance and pumping power. This metric helped to identify the best heat sink based on the thermo-fluid characteristics, i.e., the lowest core temperature with the least pumping power.

Heat Transfer and Pressure Drop Measurements in a High Aspect Ratio Channel With Circular Pins and Strip Fins

Abstract This paper focuses on the measurements of heat transfer enhancement and pressure drop of different pin or fin configurations in a high aspect ratio (AR = 9.57/1.2) channel. Two different pin-fin shapes including circular pins and strip fins were studied. Different pin-fin spacings for circular pins (S/D = 2, 4) and strip fins (S/W = 8, 16) were investigated, respectively. In addition, the thickness effect of the strip fin was included in this study. The regionally averaged heat transfer measurement method was used to acquire the heat transfer coefficients on two opposite featured surfaces within the test channel. For each configuration, the tested Reynolds number was ranging from 20,000 to 80,000. The results indicate that the channel with circular pins has better heat transfer enhancement and higher pressure loss than their strip fins counterparts. However, the strip fins are considered better designs in terms of thermal performance. For the gas turbine designers aim at developing an improved internal cooling feature, this work demonstrates the great potential of the strip fins as a novel and effective cooling design compared with the conventional circular pins.

A transient study on two phase adiabatic flow over micro circular pin heat sinks

In the present work, a transient numerical study on two-phase flow over circular staggered and inline micro pin fins is conducted. Pin diameter, fluid density ratio, and surface tension have been taken into account. Diameters of micro pins are in the range of 50 to 250μm; moreover, a variation of 100 fold in the surface tension and density ratio are considered. In order to solve the numerical model of a micro heat sink, a volume of fluid (VOF) method using open package Gerris Flow Solver (GFS) is employed. Pressure drop, flow velocity, as well as void fraction for all cases are presented and discussed. Based on the results, transient nature of flow is observed even after the first transition phase. Flow mixing as an essential phenomenon in heat transfer is thoroughly discussed. Our study proves that with an increase of pin diameter the flow mixing near micropins is hindered. Moreover, bridge formation in staggered conformation was observed which may reduce the heat transfer. Additionally higher surfaces tension ratio yielded a better flow mixing.

The influence of tip clearance and shape of pin fins on the heat transfer performance and friction factor in aluminum silicon alloy heat exchanger

In this article, the coupled heat transfer model was applied to investigate the effect of the tip clearance and shape of pin fins on the heat transfer performance and friction factor in the high temperature region of aluminum silicon alloy heat exchanger. The tip clearance ranged from 1 mm to 8 mm, and the shape of pin fins was the circular, drop-A and drop-B. The results showed that as the tip clearance increases, the outlet flue gas temperature increases, while the Nusselt number, the pressure loss and the friction factor decreases. For the circular pin fin, the difference of outlet flue gas temperature between it and drop-A was very slight, but both were higher than drop-B. In addition, circular pin fin had the minimum values of pressure loss friction factor. Comprehensively considering the heat transfer performance and friction factor, the thermo-hydraulic performance of circular pin fin with the tip clearance of 4 mm was superior to other cases.

Role of nano-fillers on tribological behaviour of ultra high molecular weight polyethylene composites

An investigation has been made of the dry slithering wear and two-body abrasive wear (2-BAW) performance of ultra high molecular weight polyethylene (UHMWPE) loaded up with carbon nanotubes (CNTs) and copper nanoparticles (n-Cu). Tribological tests were carried out utilizing a pin-on-disc test rig employing EN32 steel and SiC emery paper as counterparts against UHMWPE composite glued to a circular pin, under different test circumstances. Scanning electron microscopy (SEM) was expended to dissect the morphologies of chosen worn surfaces. The configurations of friction coefficient (µ), weight reduction and explicit wear rate (Ks) were assessed in adhesive wear-mode and the Ks in the event of multi-pass 2-BAW mode under various dissociate/masses. It has been demonstrated that inclusion of exceptionally little extents (0.1 and 0.5 wt%) of nano-fillers has resulted in significant improvement in the slithering wear performance. Moreover, 1-D filler (CNTs) diminished the contact surface, advanced the exchange of UHMWPE and diminished the interlocking and furrowing of the composite from the steel partner, which added to the reduction of both Ks and µ. UHMWPE loaded up with 0.5 wt% CNTs has outpaced the material system in the study group in tribological properties. Abrasive wear assessment revealed that the UHMWPE composites demonstrated diminished Ks with expanding abrading distance and coarseness of SiC emery paper. Further, UHMWPE/CNTs demonstrated good resistance to abrasion wear in contrast with unfilled UHMWPE and n-Cu filled UHMWPE composites.

Heat Transfer Analysis of Solid and Perforated Fins in Regular Arrangement

Extended surfaces are widely used in various applications like aerospace parts design, cooling and also in solar collectors for effective dissipation of heat. The present paper gives us an idea about the heat transfer analysis for solid pin fin and perforated pin fins that are fitted in a rectangular chamber. The rectangular chamber has a cross section area of 300 * 200 mm2. It is concluded from the experiment that perforated pin fin always works better as compared to solid pin fin in all conditions. Moreover, for lower range of Reynolds number, solid pin fin performs better whereas for higher range of Reynolds number, perforated pin fin performs better as compared to circular pin fin.

CFD analysis of employing a novel ecofriendly nanofluid in a miniature pin fin heat sink for cooling of electronic components: Effect of different configurations

This research aims to study the thermal and hydraulic attributes as well as energy efficiency of a new ecofriendly nanofluid including functionalized graphene nanoplatelets in a mini heat sink with three different pin fins. The circular, triangular and drop-shaped pin fins are investigated and compared with each other. The effects of nanoparticle fraction and flow velocity on the thermal resistance, temperature uniformity, convective heat transfer coefficient, maximum surface temperature, average surface temperature, pressure loss and pumping power are assessed. Increasing the concentration or velocity reduces the temperature on the heated wall, and also improves the temperature distribution uniformity. At both constant velocity and invariant pumping power, the heat sink fitted with the circular pin fins leads to the best performance while that equipped with the triangular pin fins results in the worst efficiency. In addition, the Figure of Merit (FoM) is greater than 1 for all conditions, which proves that the nanoparticle suspension possesses a greater merit to be employed as the coolant in the heat sinks compared to the base fluid.

X-ray computerized tomography for characterization of pick-up destruction and pick-up parameter optimization of tomato root lumps

This study was aimed to find the causes of pick-up destruction of tomato root lumps using X-ray microcomputed tomography, and to identify the pick-up parameters of low root lump destruction. The roots and pores were reconstructed three-dimensionally and analyzed quantitatively. It was found that the roots acted winding and wraping the root lumps and thus preventing the substrate from loosening. The major causes for root lump destruction were pore aggregation and crack formation. The apex and circumference of pick-up pins were areas where root lumps were prone to fracture and breakage, respectively. Lacunarities of these two areas were used as index to quantify the root lump destruction. Single-factor analysis of variance was conducted with pick-up pin shape (circular, flat), diameter (2, 2.5, 3 mm) and initial pick-up angle (18°, 21°, 24°) as the test factors and then the effects of these three factors on root lump destruction were studied. It was found the lacunarities at the fracturable area and breakable area both increased with the rise of pick-up pin diameter and decreased with the rise of initial pick-up angle. At the same pick-up conditions, lacunarities with the use of flat pins always surpassed that of circular pins. When circular pick-up pins with diameter of 2 mm and initial pick-up angle of 24° were used, the destruction rate of root lumps (6.63%) was smaller than under other test conditions. The optimized pick-up parameters can be used to guide gripper design and to improve the working performance of automatic transplanters.

The hydraulic‐thermal performance of miniature compact heat sinks using SiO2‐water nanofluids

AbstractEver since the rapid increase in both the demand for the miniature electronic devices and their applications, heat dissipation in the electronic components has been a serious issue. A miniature plate‐pin heat sink model with square, circular, and elliptic pins is considered to enhance the hydrothermal performance of this kind of compact heat sink (CHS). Water and 3% of SiO2‐water nanofluids of volume fraction were used with different Reynolds number ranges (100‐1000). The findings show that the base temperature of heat sink reduces while the Nusselt number enhances by using nanofluids and increasing Reynolds number. The lowest value of the base temperature is nearly 25% for the square pins and circular pins CHSs compared with a plate–fin heat sink at 3% of nanofluids. Furthermore, the highest value of the Nusselt number is about 98% at 3% SiO2 for circular pin CHSs compared with the plate–fin heat sink. However, the pressure drop of CHSs is higher than that of plate–fin heat sink. Moreover, the most significant hydrothermal performance value is about 1.44 for water and around 1.51 for SiO2 as using the CHS with circular and elliptic pins depends on the Reynolds number. Thus, applying CHSs with nanofluids instead of the traditional heat sinks might produce a substantial enhancement in the hydrothermal performance of heat sinks.

Investigation of tensile strength on friction stir welded joints of dissimilar aluminum alloys

Abstract The main aim of this paper is to study the feasibility of friction stir welding of AA6061-T6 & AA6082 and to examine the effect of process parameters like geometry of the tool pin, rotational speed of the pin, welding speed and tilt angle on tensile strength of welded joints. Experimental results based on Taguchi method confirm that tool rotational speed has major contribution to tensile strength as compared to speed and tilt angle in case of both circular and square pins. The welded joints produced by circular pin show superior strength of the joint than that of the square pin.

Stress concentration and optimal design of pinned connections

A pinned connection or lug joint is a common connection type used both in civil engineering and mechanical engineering. In civil engineering, this connection is used for assembling truss members, and in mechanical engineering, this connection type is widely used in machine elements. The standard design is with a circular pin. The stress concentration factor size depends on the tolerances between pin and assembled parts and also by the three-dimensional design. Relatively different maximum stress values are seen depending on the modelling being done in two dimension (with assumptions) or in full three dimension. The focus in the present article is on the two-dimensional design and minimizing the maximum stress. It is shown that not only the contact geometry is important for reducing the stress, the external design is equally important. By finite element analysis including contact modelling, it is shown that reduction in the stress concentration factor of up to 18% is possible.

Effects of Pin-Fin Shapes on Mesh-Fed Slot Film Cooling for a Flat-Plate Model

Experimental and numerical research is performed to illustrate the effects of pin-fin shapes on mesh-fed slot film cooling performance on a flat-plate model. Three types of pin-fin shapes (such as circular, elliptical, and drop-shaped) with the same cross-sectional area are taken into consideration. The results show that a pair of counter rotating vortices is still generated for the mesh-fed slot film cooling scheme due to the strong “jetting” effect of coolant flow at the slot outlet. As the coolant jet ejecting from mesh-fed slot is capable of establishing more uniform film layer over the protected surface, the kidney vortices are illustrated to have weakly detrimental role on the film cooling performance. By the shaping of pin fins, the uniformity of coolant flow exiting mesh-fed slot is improved in comparison to the baseline case of circular shape, especially for the elliptical-shape pin-fin array. Therefore, the jetting effect of coolant flow is alleviated for the elliptical and drop-shaped pin-fin meshes when compared to the circular pin-fin mesh. In general, the pin-fin shape has nearly no influence on cooling effectiveness immediately downstream the film cooling-hole outlet. However, beyond x/s = 5, the elliptical and drop-shaped pin fins are demonstrated to be advantageous over the circular pin fins.

Control of Flow Separation over a Flapped Airfoil Using Low-Aspect-Ratio Circular Pins

The implementation of an array of finite-span, low-aspect-ratio circular pins as a flow control method to mitigate separation over a flapped airfoil was investigated experimentally in a wind tunnel. The effect of an array of static cylinders, placed just upstream of a deflected control surface, on the separated flow over the control surface was explored via surface pressure and stereoscopic particle image velocimetry measurements. The array of pins was embedded in a turbulent boundary layer, where the height of the pins was approximately 2/3 of the local boundary-layer thickness. The static array of pins demonstrated a large reduction of the separated flow over the control surface, as well as a change in the global circulation, quantified by an enhanced sectional lift coefficient of and reduction in drag coefficient of . A secondary dataset was collected, which studied the effect imposed on the nearfield from a single pin that was either static or underwent dynamic motion (in the wall-normal direction), placed upstream of the deflected control surface hinge line. Results indicate that even a single pin (with diameter-to-airfoil span ratio of ) had a noticeable impact on the delay of separation, enhanced global circulation, and drag reduction. Overall, the features discussed have provided strong evidence of the potential that finite-span, low-aspect-ratio cylindrical pins provide as new actuators for flow control.

Flow Structure and Heat Transfer Characteristics of a Rectangular Channel With Pin Fins and Dimples With Different Shapes

Abstract In this study, numerical simulations are conducted to investigate the effects of pin fin and dimple shape on the flow structure and heat transfer characteristics in a rectangular channel. The studied shapes for dimple and pin fin are circular, spanwise-elliptical, and streamwise-elliptical, respectively. The flow structure, friction factor, and heat transfer performance are obtained and analyzed with Reynolds number ranging from 10,000 to 50,000. Channel with circular pin fin and dimple is chosen as the Baseline. Channels with spanwise-elliptical pin fins have the best heat transfer augmentation, while also accompanied with the largest friction factor. Spanwise-elliptical pin fin generates the strongest horseshoe vortex which is responsible for the best heat transfer augmentation. Besides, channels with streamwise-elliptical pin fins show the worst heat transfer augmentation and the smallest friction factors. Dimple plays an important role in improving the heat transfer. Spanwise-elliptical dimple yields the best heat transfer augmentation which is attributed to the strongest counter-rotating vortex, while streamwise-elliptical dimple shows the worst heat transfer enhancement.